So what is back button focusing?
It’s a very simple thing that might change the clarity of your images forever.
When you auto-focus with your DSLR default settings, here is how it basically works: you press your shutter half way to auto-focus, and when your focus is OK you press your shutter a second time to take the picture. There is an alternative to this focusing method: you can decide that another button (the famous BBF, or “back button focusing”) will handle your focus.
Depending on your camera, you can use the AF-ON button (this is the one I am using on my Canon 5D MarkII), or the AF-L button for Nikon users, or even the star (*) button.
Why would you do that?
Simply because it separates your focusing from your shutter. Instead of asking your index finger to deal with two different things one after the other, you give it one single task (pressing the shutter at the perfect moment) while your thumb will deal with focusing.
There is a debate about BBF. Some have tried it and swear that they don’t see any difference. If you mainly photograph landscape or still life, it’s very likely that BBF won’t change your life. On the other hand, if you are a portrait photographer, and if your model is potentially moving fast (those who have a toddler at home, I can feel your attention growing!!), BBF is probably going to be your best friend.
Let’s try to understand why. Here is an image of two cute boys playing knights. They’re happily running towards the lens.
If you place your focal point on the first boy, press your shutter half way to focus and then press the shutter, there is a fraction of seconds between those two steps. This very short moment can be long enough to let the first boy step out of your focus zone. Especially if you were using a wide aperture, thus having a very shallow depth of field. As a result, you will get an unsharp image.
Fortunately, I was using BBF when I took this image (I use it all.the.time). I was also using a dynamic autofocus mode (Ai-Servo, the equivalent is AF-C if you are a Nikon user). Thus, I kept my thumb on the back button all the time, allowing my camera to continuously autofocus and follow the boy’s movement. When my index hit the shutter, my thumb was still pressing the back button so both actions happened simultaneously. As a result, my focus was spot on.
So BBF will guarantee a more precise focusing with any image involving a fast movement, like Hayden flying in the air or Etan jumping.
This is why BBF is very often used by sports photographers, or wildlife photographers (in order to capture a flying bird for example).
Note: this article is not covering all the aspects leading to sharpness, but don’t forget that to get a crisp image with a fast moving subject you also need a high shutter speed in order to freeze motion, like 1/500s or 1/640s in the two examples above.
Another interest of BBF is that it locks your focus.
If you press your thumb on your back button and release it, your focus won’t change until you press the button again. This is something that I use a lot with my recent self-portrait project.
Let’s look at this image of my sons and me:
I placed my camera on a tripod in front of my bed. I asked my sons to sit on the bed, and used them as targets to meter and focus. Once my exposure and focus settled, I didn’t touch my camera anymore. I joined them on the bed (making sure I was standing close to the focal plane they were in when I focused), and the only thing I had to do is snuggle with them and snap away with my remote. We took a series of 10 images without having to care about anything else than having fun, my focus was locked so I knew it would remain faithfully where I wanted it to be!
How do I start?
How to set BBF depends on your camera, so check your user manual.
On my Canon 5D Mark II menu, it is found in custom function IV (C.FnIV), and I selected the 3rd option (AE Lock/Metering + AF start).
If you are a Nikon user, you should go into your custom settings menu, select A (autofocus), select A5 (AF Activation) and then choose AF-ON only.
For those of you already using BBF and loving it, please share your settings in the comment section of this article to help new users find the right path!
So, now it’s your turn! Switch to BBF and play to your heart’s content. You might need a few days to get used to it, but soon enough you will wonder how you could live without it! I swear it’s worth trying because I’ve been nailing my focus ever since I discovered it.
Lisa Tichané, France